Antimicrobial Resistance Study Finds No mcr-1 Gene Presence in France

When researchers recently discovered a strain of Escherichia coli resistant to the final resort antibiotics colistin and carbapenem in the United States, it marked an increasing pattern of pan—drug-resistant bacteria appearing worldwide. A new report from France, though, may indicate that identifying and isolating these deadly superbug strains may help us control their spread.

The recent French study analyzed carbapenemase-producing Enterobacteriaceae isolates collected from colonized or infected patients from January 2014 to December 2014, as part of a national survey on antimicrobial resistance. Published in the infectious disease epidemiology, prevention, and control journal Eurosurveillance, the paper details findings on a total of 972 bacterial isolates taken from rectal, stool, urine, respiratory tract, blood, wound, catheter, and vaginal swabs. Of those, there were 577 isolates of Klebsiella spp., 236 of Escherichia coli, 108 of Enterobacter spp., 50 of Citrobacter spp., and a single Salmonella spp. isolate. Researchers conducted the study in response to France’s lack of information on the epidemiology of colistin resistance among enterobacterial isolates in the country, and due to worldwide concerns about the plasmid-mediated mcr-1 gene encoding colistin resistance.

Antimicrobial resistance is a topic dominating hospitals and international health meetings alike. As bacterial and viral pathogens continue to develop into new strains that defy medical treatment, infections that were once easily treatable can today become deadly. In the new study out of France, scientists analyzed the isolate samples for their characterization and drug resistance mechanisms. Their antibiotic susceptibility aimed to determine each isolate’s minimum inhibitory concentrations of colistin. The researchers found that of the 561 isolates of Klebsiella pneumoniae testing, 35 (6%) isolates showed colistin resistance, with the mgrB gene that is the source of colistin resistance of K. pneumoniae and Enterobacter. Another 15 isolates harbored both the carbapenemase gene as well as the extended-spectrum beta-lactamase (ESBL) gene conferring drug resistance. Of the 91 Enterobacter cloacae isolates, seven were resistant to colistin (7.7%), with a single carbapenem-resistant E. asburiae strain showing resistance to colistin.

Overall, among the samples, the researchers found that the rate of colistin resistance among the carbapenemase-producing isolates were 7.7% for Enterobacter spp. and 3.6% for K. pneumoniae isolates. These show a much lower rate than has been identified in Spain and Italy, where the resistance rate observed among the carbapenemase-producing K. pneumoniae isolates is 20% and 43%, respectively.

The study researchers were surprised to find no colistin resistance in any of their 236 E. coli or 50 Citrobacter isolates, and no sight of the resistance gene mcr-1. A previous French survey of isolates collected from veal calves found mcr-1 in 21% of ESBL-producing E. coli isolates. Likewise, neighboring countries have in recent years discovered mcr-1 — in isolates recovered from river water and imported vegetable samples in Switzerland, in E. coli isolates from calves and piglets in Belgium, in swine and human wound infections in Germany, in food and human bloodstream infections in Denmark, and in Salmonella enterica from food samples in Portugal.

“We believe that the plasmid carrying the mcr-1 gene might be currently more prevalent among ESBL-producing isolates than among carbapenemase-producing isolates in human samples, which would explain why we did not identify this gene in our collection of carbapenemase-producing isolates,” write the authors, noting the good news found in their study. “These resistance rates remain much lower than those observed in other European countries such as Greece, Italy and Spain. No plasmid-encoded mcr-1 gene was identified here. Therefore, it seems that it is still possible to control the spread of those multidrug-resistant isolates based on accurate identification of colistin resistance and isolation of plasmid-encoded MCR-1 producers.”